Monitor 5jr upgrade question

punk-roc

So, I'm taking a look at the Monitor 5jr xover's I have in order to practice my modding skills before taking on my SDA-2's and Monitor 5-A's...

These 5jr's i got from Doro didn't come on a pcb.. just hot glued into the center of large plastic circular piece that holds the fuse, speaker terminals, etc.



Now I don't know anything about capacitors, etc, but thought i would get it down with pictures and reading the board..

I know the 5jr's are simple, but is this the only piece i need to change out? I just don't know what I'm looking at in here, lol



Thanks guys, not enough threads with pictures for dummies like me...

Jason

Outfitter03

Since I am not living in Mamby, Pamby land today I will give this a shot.

There are two components that you want to trade out in this upgrade. The tweeter resistor and tweeter cap. There are several schematics in the vintage section for Monitor 5jr, although none showed a fuse that you mentioned.

To confirm what you need to order you will need to clear enough of the hot glue off of the resistor to read the value. This should be the white rectangular object under the cap. Per the print it should be a 1.3 ohm 5w resistor, but may be a 1.0 ohm resistor. If the printing is not legible you will need to measure it's value with an ohm meter. Once you know the value you can order two new ones. Most Polkies use the Mills resistors from Sonic Craft or Parts Express and many recommend going to 10W power rating for a couple bucks more.

The other component to replace is the capacitor which should be 12uF. In the picture posted you can just make out the units uF. Hopefully in front of that is a 12.

Under all the hot glue you should discover wires running your signal path like this: + terminal of binding post to a lead on the buried resistor > opposite lead on resistor to wire on bottom of capacitor > top lead of capacitor T connected to .19mh inductor and chassis wire running to tweeter. The last connections are visible in the picture.

Since you are not working on a PCB with this crossover, when you order the components it would be a good idea to get a little extra chassis wire to make your connections because you are building a point to point crossover and may need a little more wire than is supplied on the end of the resistors or capacitors.

Systems

Since I am not living in Mamby, Pamby land today I will give this a shot.

Denial is not just a river in Egypt!:biggrin:

Systems

pepster wrote: »

Denial is not just a river in Egypt!:biggrin:

You know being a smart a$$ is a skill like anything else!:biggrin:

Thats some good advice Outfitter.
There are TONS of info on this sight for those particular x-overs.
Might want to drop Ben a pm to discuss your options.

punk-roc

thanks outfitter.. I thought I would need to dig that white resistor thing out of the glue..

ben62670

What is the value on the Black cap?

punk-roc

ben62670 wrote: »

What is the value on the Black cap?

12uF - 50VAC

ben62670

What do the resistors say?

punk-roc

i haven't gotten the resistor excavated yet.. its face down in the glue and i can't see the value on it.

I've been being super careful since I'm not real clear on how everything goes together, so i didn't want break a wire off when i didn't know where it went hahaha.

Jason

ben62670

Just don't tear both apart. You'll be OK It looks like both are paralel so you can replace it with one resistor. Can you measure the resistance with a multi meter?

punk-roc

i don't have a multi meter yet unfortunately.. just a voltage meter.

Thanks for helping Ben. I've been meaning to get a multi meter.. I don't have time today, but I was going to dig the rest of the resistor out of the glue tomorrow and get everything figured out

So that white box is really two resistors, not just one?

ben62670

It certainly looks like two resistors.

punk-roc

so, i got the resistors excavated.. it looks like they are in parallel, one is 2.5ohm 10% 5W and the other is 2.7ohm 10% 5W..

here's a picture for clarity



So, not being an electronics person.. what could i replace these with? could i just get one resistor? or i could just buy two of the same type i'm assuming..

Thanks Ben, et al.

Jason

dorokusai

I have a pair of mint grills for those if you're interested....complete with Polk emblems.

punk-roc

i actually got some really nice, mint grills with my monitor 5As.. thank you for the offer though Mark.

Random side note, can i use these 5jr crossover's in those 5As? just trying to figure out if i can actually test my work at the end but this has been a good experience either way though

dorokusai

Cool, just figured I'd ask as I just moved them today while looking for someone else. There's very little difference between the two models, so much so that you should look closely at the xover schematic.

punk-roc

will do, thanks Mark.

Outfitter03

punk-roc wrote: »

So, not being an electronics person.. what could i replace these with? could i just get one resistor?

Jason

Easy calculation to do with one of many parallel resistor calculators:

http://www.1728.com/resistrs.htm

The calculated value is 1.298 ohms. The calculated tolerance given the resistors 10% tolerance is 1.17 to 1.43 ohms. The crossover schematic specifies a target of 1.3 ohms. You could use two MRA-5 or two MRA-12 with the same values as found in the crossover. You could also use a single 1.2 ohm MRA-12 if accuracy is not that important to you. This is outside of the 5% tolerance though, which is a good rule of thumb for deciding acceptable values.

http://www.soniccraft.com/mills_resistors.htm

punk-roc

Thanks Outfitter, I'll take a look.. I'd rather do it right than easy, just gotta figure out what right is

Jason